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This application is a continuation of application Ser. No. 08/478,093, filed Jun. 7, 1995, now U.S. Pat. No. 5,877,897, which is a continuation-in-part of International Patent Application No. PCT/US94/01954, which designates the United States and which was filed Feb. 25, 1994 and which is a continuation-in-part of U.S. patent application Ser. No. 08/023,918, filed Feb. 26, 1993, now U.S. Pat. No. 5,550,677.
an imaging device for capturing an image of a front seat of an interior of the vehicle and outputting image data corresponding thereto;
a processor which (i) receives the image data output from the imaging device, (ii) compares the received image data with stored image data, and (iii) outputs a vehicle equipment control signal based on the comparison; and
said processor modifying said stored image data in accordance with a light level present in said interior of said vehicle, thereby rendering said apparatus substantially insensitive to general lighting conditions, said apparatus being sensitive to movement within said interior of said vehicle.
an imaging device disposed in a front portion of a vehicle compartment for imaging a front seat of said vehicle compartment and outputting image information corresponding to occupancy of the vehicle front seat;
a processor which (i) receives the image information from the imaging device, (ii) compares the received image information with stored image information corresponding to the vehicle front seat, and (iii) outputs an inhibit signal inhibiting activation of the airbag when the comparison determines the occupancy of the vehicle front seat is within a predetermined class; and
said processor modifying said stored image information in accordance with a light level present in said vehicle compartment, thereby rendering said apparatus substantially insensitive to general lighting conditions, said apparatus being sensitive to movement within said vehicle compartment.
1. Field of the Invention
This invention relates to an automatic rearview mirror system for automotive vehicles which automatically changes reflectance level in response to glare causing light, and more particularly relates to an improved automatic rearview mirror system using only a rearwardly facing sensor. This invention further relates to an automatic rearview mirror and vehicle interior monitoring system for automotive vehicles which also monitors a vehicle interior or compartment. This invention further relates to an automatic rearview mirror and vehicle interior monitoring system for automotive vehicles which may also be used as a vehicle intrusion detection system or as a compartment image data storage system. This invention further relates to an automatic rearview mirror and a vehicle lighting control system using an image sensor, such as a photosensor array.
2. Description of Related Art
Automatic rearview mirrors and mirror systems have been devised for varying the reflectance level of a variable reflectance rearview mirror by reducing the reflectance automatically in response to annoying glare light, as seen rearwardly of the rearview mirror or mirrors by a driver of the vehicle, and by increasing automatically the reflectance to a normal or maximum reflectance level when the annoying glare light subsides. These automatic mirrors have been changed over the years in an effort to improve their performance characteristics and associated level of glare protection.
Early automatic rearview mirrors used a rearwardly facing sensor and control circuit to change mirror reflectance. One example of such a "single-sensor" type mirror is described in U.S. Pat. No. 4,266,856. In these prior art single-sensor type mirrors, the rear glare light was incident on a rearwardly facing sensor or photocell, such as a photodiode, photoresistor or phototransistor. These mirrors suffered from various problems, however, including the problem that these mirrors would become increasingly sensitive and even "lock-up" in their minimum reflectance level or state as the driver encountered significantly higher light levels in town or city driving. This required the driver to repeatedly adjust the mirror's sensitivity control to prevent such problems.
To overcome the problems of single-sensor type mirrors, a non-rearwardly facing photocell for sensing "ambient" light was added. It was believed that the desired reflectance necessary to relieve the driver from glare depended not only on glare light but also on ambient light. Accordingly, these "two-sensor" type mirrors used two separate photocells, one generally facing rearwardly and one generally facing forwardly (or other non-rearwardly facing direction) of the mirror or vehicle. The signals from these two photocells were then compared in some fashion, and when, for example, the glare light from the rear was comparatively high with respect to the "ambient" light, a control circuit would apply a control signal to reduce mirror reflectance. Some examples are described in German Laid-Open Patent No. 3,041,692; Japanese Laid-Open Patent No. 58-19941; and U.S. Pat. Nos. 3,601,614; 3,612,666; 3,680,951; 3,746,430; 4,443,057; 4,580,875; 4,690,508; and 4,917,477. In many of these prior art automatic rearview mirrors, light generally forward of the mirror or vehicle was incident on the second photocell.
These arrangements, however, also had problems. In some of these mirrors the forwardly facing or "ambient" light sensor was inaccurate because it did not correctly measure ambient light levels since it did not include light generally rearward of the mirror or vehicle. Some examples include the devices described in U.S. Pat. Nos. 4,443,057 and 4,917,477. Other prior art devices overcame these deficiencies by providing a control circuit which correctly measured ambient light as a combination of both the forward and rear light levels. Examples of this significantly different approach are described in U.S. Pat. Nos. 4,793,690 and 4,886,960.
prior art two-sensor type systems generally provided improved performance over prior art single-sensor type systems but were also more complex and costly. In part, this was because using separate forwardly and rearwardly facing photocells required that the performance characteristics of the two separate photocells, such as photoresistors, be matched appropriately to ensure consistent performance under various operating conditions. Matching photocells such as photoresistors, however, generally involves complex, expensive and time consuming operations and procedures.
Both the prior art single-sensor and two-sensor type mirrors presented additional problems when they were also used to control the exterior side view mirrors. This is because such prior art systems used a common control or drive signal to change the reflectance level of both the interior rearview mirror and the exterior left and/or right side view mirrors by substantially the same amount. In U.S. Pat. No. 4,669,826, for example, a single-sensor type mirror system used two rearwardly facing photodiodes to control both an interior rearview mirror and the left and/or right side view mirrors based on the direction of incident light from the rear. Another example includes the two-sensor type system described in U.S. Pat. No. 4,917,477.
In rearview mirror systems, however, each of the interior rearview and exterior side view mirrors may reflect different source light levels. More specifically, the inside rearview mirror, left side view mirror and right side view mirror each enable the driver to view a different portion or zone of the total rearward area. Of course, there may be some overlap of the image information contained in each of the three zones. The situation is further complicated with multi-lane traffic because each of the mirrors reflects different light levels caused by the headlights of the vehicles which are following, passing or being passed. As a result, in the prior art systems, when the reflectance level of the interior rearview mirror was reduced to decrease the glare of headlights reflected therein, the reflectance level of the exterior left and right side view mirrors was also reduced by substantially the same amount, even though, for example, the side view mirrors might not be reflecting the same level of glare light, if any. Accordingly, rear vision in the exterior left and right side view mirrors could be improperly reduced.
Other prior art two-sensor type systems used a common ambient light sensor and several rearwardly facing sensors, one for each of the mirrors. An example is the alternate system also described in U.S. Pat. No. 4,917,477. This approach is not satisfactory, however, because it reduces system reliability and increases complexity and cost.
Finally, some prior anti-glare mirrors used several sensors to control the segments of a variable reflectance mirror. One example is disclosed in U.S. Pat. No. 4,632,509, which discloses a single-sensor type mirror using three rearwardly facing photocells to control three mirror segments depending on the direction of incident light from the rear. See also U.S. Pat. No. 4,697,883. These prior mirror systems generally have the same problems as the other single-sensor type mirrors. Some other anti-glare mirrors are generally disclosed in U.S. Pat. Nos. 3,986,022; 4,614,415; and 4,672,457.
Consequently, there is a need for an automatic rearview mirror system for an automotive vehicle having improved reliability and low cost, which accurately determines or otherwise discriminates light levels that the driver will experience as glare without the need for a separate forwardly facing photocell. In addition, as noted above, there is also a need for an automatic rearview mirror system of high reliability and low cost, which accurately determines light levels that the driver will experience as glare, and which can control independently the reflectance of a plurality of mirrors according to the light levels actually reflected by each of the rearview and exterior side view mirrors without the need for additional and separate rearwardly facing photocells. There is also a need for an automatic rearview mirror system that can independently control the segments of a variable reflectance mirror while accurately determining light levels that the driver will experience as glare in each segment of the mirror without the need for additional and separate forwardly and rearwardly facing photocells.
One concern with automatic rearview mirror systems, as well as other systems having sensing, control or logic circuits located in the rearview mirror, is that differences in vehicle design and mirror field of view requirements may result in rearview mirrors having a variety of appearances (or finishes), forms (or shapes) and sizes. These variations generally require the re-design and re-tooling of a number of the components or sub-assemblies of the rearview mirror head assembly. However, it is generally desirable to reduce the number of components or sub-assemblies of the rearview mirror head assembly so as to reduce cost, product development lead time and manufacturing complexity. To achieve this in automatic rearview mirrors, as well as other systems having sensing, control or logic circuits located in the rearview mirror, it is desirable to locate the sensing, control or logic circuits and related components in a housing or module, which is attached, connected, made integral with or otherwise associated with the rearview mirror mounting bracket means or structure so that a common design of a mounting bracket sub-assembly for a rearview mirror may be used with a variety of rearview mirror head assemblies.
Vehicle lighting systems may include a variety of vehicle lights, including low intensity peripheral or side lights that allow other vehicle drivers to see the vehicle in lower light conditions, high intensity headlights that operate in a low beam mode or a high beam mode for general night driving, and fog lights that provide low ground lighting with less back scattering to improve the driver's views in adverse weather conditions, such as fog, rain and snow. Vehicle lighting systems may also include headlights having an intermediate or mid beam mode, as well as the low and high beam modes. Vehicle lighting systems may also include vehicle running lights, which are vehicle headlights that are operated at an appropriate intensity to improve the ability of other vehicle drivers to see the vehicle during the day. Vehicle running lights may also be used for lower lighting conditions, such as certain adverse weather conditions or other lower visibility conditions.
Thus, as the number of vehicle lighting options has increased, it has become more complex for the driver to determine the appropriate vehicle lighting configuration and to operate or control the vehicle lighting systems. Therefore, improved vehicle lighting control systems are required that may operate with other systems, such as automatic rearview mirror systems and vehicle interior monitoring systems, or as stand-alone systems.
Finally, unauthorized vehicle intrusion for the purpose of stealing the vehicle or its contents is a significant problem. Each year, automotive manufacturers are including vehicle anti-theft or intrusion detection systems on more vehicles to deter potential intruders and to prevent the theft of vehicles or their contents. Currently known vehicle anti-theft systems are generally designed to protect the vehicle or its contents from theft or vandalism. There are many versions of vehicle anti-theft systems using various sensor technologies that attempt to deter theft or vandalism using the horn, siren or flashing lights, or other alarm mechanisms to bring attention to a vehicle. As is known, existing intrusion detection systems for vehicles use sensor technologies that have various limitations, including the problem of false triggering. For example, in many cases active vehicle alarms are simply ignored by people who assume that the alarm was falsely triggered. The proliferation of separate automatic rearview mirror systems and vehicle intrusion detection systems is also costly. Therefore, vehicle intrusion detection systems using an improved sensor technology are required that operate in combination with other vehicle systems (such as automatic rearview mirror systems) or that operate independently.
Even with such anti-theft systems, recovered stolen vehicles typically provide little or no evidence of the vehicle thief. Therefore, systems are required that provide an image of the vehicle thief that would be useful to law enforcement and the insurance industry as an aid in identifying the person(s) responsible for the vehicle theft, and that operate in combination with other vehicle systems (such as automotive rearview mirror systems) or that operate independently.
It is an object of the present invention to overcome the problems of the prior art.
It is another object of the present invention to provide an automatic rearview mirror system of improved reliability.
It is yet another object of the present invention to provide an automatic rearview mirror system that accurately determines light levels that the driver will experience as glare without the need for a separate forward facing sensor or other non-rearwardly facing photocells.
It is another object of the present invention to provide an automatic rearview mirror system of high reliability that accurately determines light levels that the driver will experience as glare, and which can independently control a plurality of mirrors or mirror segments according to different fields of view without the need for additional and separate rearwardly facing photocells.
According to one aspect of the present invention, using a photosensor array and an appropriate control circuit allows the elimination of separate forwardly facing or other non-rearwardly facing photocells, thereby allowing for lower costs and increased reliability since it is not necessary to match two separate photocells such as photoresistors.
According to another aspect, the present invention which achieves one or more of these objectives relates to a control system for controlling a plurality of variable reflectance mirrors or mirror segments which change their reflectance in response to a signal from a drive circuit. The system comprises a plurality of variable reflectance mirrors, a photosensor array and a control circuit receiving signals from the photosensor array for controlling the mirrors. The photosensor array is mountable to view rearwardly of the mirror or vehicle. The photosensor array comprises a plurality of sets of photosensor elements corresponding to the plurality of variable reflectance mirrors. The photosensor elements in each set produce a plurality of photosensor element signals in response to light incident thereon. The control circuit determines control signals, indicative of a desired reflectance for each of the plurality of variable reflectance mirrors, in response to receiving photosensor element signals from the photosensor element set for each view or zone corresponding to the rearview mirror and exterior side view mirrors and also (or alternatively) the mirror segments. The control signals control the drive circuit to cause the plurality of variable reflectance mirrors or mirror segments to assume the desired reflectance.
According to another aspect, the present invention which achieves one or more of these objectives relates to an automatic rearview mirror system for an automotive vehicle comprising at least one variable reflectance rearview mirror, and an array of sensing elements to sense light levels in an area rearward of the at least one variable reflectance rearview mirror. Each of the sensing elements is adapted to sense light levels of light incident thereon and to output an electrical signal indicative of the sensed light levels. The system further comprises a signal processor, connected to the array of sensing elements, receiving and using the electrical signals indicative of the sensed light levels from the sensing elements to determine a first electrical signal indicative of a background light level in the area rearward of the at least one variable reflectance rearview mirror and to determine a second electrical signal indicative of at least one peak light level in the area rearward of the at least one variable reflectance rearview mirror. The signal processor determines at least one control signal indicative of the desired reflectance level of the at least one variable reflectance rearview mirror from the first electrical signal indicative of the background light level and the second electrical signal indicative of the at least one peak light level. The system further comprises at least one drive circuit connected to the signal processor and to the at least one variable reflectance rearview mirror for receiving the at least one control signal and generating and applying at least one drive signal to the at least one variable reflectance rearview mirror to drive the at least one variable reflectance mirror to the desired reflectance level.
According to another aspect, the present invention which achieves one or more of these objectives relates to a control system for controlling a plurality of variable reflectance mirrors, each of which change their reflectance level in response to a drive signal from an associated drive circuit, for an automotive vehicle. The system comprises a plurality of variable reflectance mirrors, and a photosensor array mountable to face substantially towards a rear area. The photosensor array comprises a plurality of photosensor element sets. Each set comprises a plurality of photosensor elements. Each of the photosensor elements generates a photosensor element signal indicative of a light level of light incident thereon, and each of the sets corresponds to one of the plurality of variable reflectance mirrors. The system further comprises a control circuit, connected to the photosensor array, for determining and applying a plurality of control signals. Each of the control signals is indicative of a desired reflectance level for each of the plurality of variable reflectance mirrors in response to receiving the photosensor element signals from each of the plurality of photosensor element sets. The system further comprises a plurality of drive circuits connected to the control circuit and to different ones of the plurality of variable reflectance mirrors associated therewith. Each of the control signals is output to the drive circuit associated therewith, to generate and apply a drive signal to each of the plurality of variable reflectance mirrors causing each of the mirrors to assume a desired reflectance level.
According to another aspect, the present invention which achieves one or more of these objectives relates to a control system for controlling at least one variable reflectance mirror for an automotive vehicle. The system comprises photosensor array means for sensing light levels in an area rearward of the at least one variable reflectance mirror and generating photosensor array signals, means for determining a background light signal from the photosensor array signals, means for determining a peak light signal from the photosensor array signals, and means for controlling a reflectance level of the at least one variable reflectance mirror using the background and peak light signals.
According to another aspect, the present invention which achieves one or more of these objectives relates to a method of controlling the reflectance of at least one variable reflectance mirror comprising the steps of sensing light levels in an area rearward of the at least one variable reflectance mirror with an array of sensing elements, determining a background light level from the sensed light levels, determining a peak light level from the sensed light levels, and controlling a reflectance level of the at least one variable reflectance mirror using the determined background and peak light levels.
By using a plurality of photosensor element sets or sub-arrays on a photosensor array to control a plurality of mirrors and also (or alternatively) mirror segments, the mirrors may be controlled independently to vary their reflectance in accordance with the view associated with each of the photosensor element sets or sub-arrays.
According to another aspect the present relates to an automatic rearview mirror system for an automotive vehicle comprising a variable reflectance rearview mirror, a photosensor array means for sensing light levels in an area rearward of said variable reflectance rearview mirror and for generating photosensor array signals, a signal processing means for receiving said photosensor array signals and for determining from said photosensor array signals a signal for controlling said variable reflectance rearview mirror, and a mounting bracket means for attaching said variable reflectance rearview mirror to said automotive vehicle, said mounting bracket means further comprising a housing means for housing said photosensor array means and said signal processing means.
According to another aspect the present relates to a vehicle lighting control system for controlling a vehicle lighting system in an automotive vehicle comprising a photosensor array means for sensing light levels in a forward field of view and generating a set of photosensor array signals, and a signal processing means coupled to said photosensor array means for receiving said set of photosensor array signals and determining from said set of photosensor array signals at least one control signal for controlling said vehicle lighting system.
According to another aspect, the present invention relates to a control system for monitoring a vehicle interior and for controlling at least one variable reflectance mirror for an automotive vehicle. The system comprises photosensor array means for sensing light levels in an area rearward of said photosensor array means and generating at least a first set of photosensor array signals, first determining means coupled to said photosensor array means for receiving said at least a first set of photosensor array signals and determining from at least a portion of said at least a first set of photosensor array signals a first signal for controlling said at least one variable reflectance mirror, second determining means coupled to said photosensor array means for receiving said at least a first set of photosensor array signals and determining at least a first set of values indicative of said at least a portion of said at least a first set of photosensor array signals, and memory means coupled to said second determining means for receiving and storing said at least a portion of said at least a first set of photosensor array signals.
According to another aspect, the present invention relates to a vehicle intrusion detection system for detecting movement within a vehicle interior for an automotive vehicle. The system comprises photosensor array means for sensing light levels in an area including at least a portion of a vehicle interior and generating at least a first set and a second set of photosensor array signals, determining means coupled to said photosensor array means for receiving said at least a first set and a second set of photosensor array signals and determining at least a first set and a second set of values indicative of said at least a first set and a second set of photosensor array signals, and comparing means coupled to said determining means for receiving said at least a first set and a second set of values indicative of said at least a first set and a second set of photosensor array signals and comparing said at least a first set and a second set of values to generate at least one output control signal indicative of the correlation between said at least a first set and a second set of values.
According to another aspect, the present invention relates to a compartment image data storage system for an automotive vehicle. The system comprises photosensor array means for sensing light levels in at least a portion of a vehicle compartment and generating at least a first set of photosensor array signals, determining means coupled to said photosensor array means for receiving said at least a first set of photosensor array signals and determining at least a first set of values indicative of said at least a first set of photosensor array signals, and memory means coupled to said determining means for receiving and storing said at least a first set of values indicative of said at least a first set of photosensor array signals.
These and other objects, advantages and features of the present invention will be readily understood and appreciated with reference to the detailed description of preferred embodiments discussed below together with the accompanying drawings.
FIG. 1A is a drawing of an automatic rearview mirror of the present invention, including an expanded view of a rearwardly facing photosensor array located in the upper center area of the mirror surface;
FIG. 1B is another drawing of an automatic rearview mirror of the present invention, including an expanded view of the rearwardly facing photosensor array alternatively located in a bezel or chin of the mirror;
FIG. 1C is a diagram of an automatic rearview mirror of the present invention, in which the photosensor array and logic and control circuit are located in a housing or module that is attached, connected, made integral or otherwise associated with the rearview mirror mounting bracket structure;
FIG. 1D is a side sectional view of the automatic rearview mirror of FIG. 1C;
FIG. 2 is a drawing of an automotive vehicle with the automatic rearview mirror system of the present invention;
FIG. 2A is an illustrative diagram of a rearward area of a vehicle interior as viewed by the photosensor elements of the photosensor array for monitoring the vehicle interior;
FIGS. 3A and 3B are illustrative diagrams of a rearward area as viewed by the photosensor elements of the photosensor array;
FIG. 4A is generalized diagram of a photosensor array PA(N,M) having a sub-array S(X);
FIG. 4B is a generalized diagram of the photosensor array PA(N,M) and sub-arrays S(0), S(1), S(2) and S(3);
FIG. 5 is another schematic diagram of the photosensor array commonly located on a light sensing and logic circuit;
FIG. 6 is a schematic block diagram of the automatic rearview mirror system;
FIG. 6A is a schematic block diagram of the automatic rearview mirror and vehicle interior monitoring system;
FIG. 6B is a schematic block diagram of a vehicle lighting control system having a photosensor array that has a forward field of view;
FIG. 7 is a flow chart illustrating the method of the present invention for controlling the reflectance of a rearview mirror or mirrors;
FIGS. 8A and 8B are detailed flow charts for steps S150, S160 and S180 of FIG. 7;
FIG. 9 is a flow chart of the general logic flow of
FIGS. 7, 8A and 8B for controlling the reflectance of three mirrors;
FIG. 10 is another schematic block diagram of the automatic rearview mirror system of the present invention;
FIG. 10A is a schematic block diagram of the automatic rearview mirror and/or vehicle interior monitoring system of the present invention;
FIG. 11A illustrates the normalized spectral response of the photosensor array made using a non-epitaxial silicon process;
FIG. 11B illustrate the normalized spectral response of the photosensor array made using an epitaxial silicon process;
FIG. 12 is a flow chart illustrating the method of the present invention of the vehicle interior monitoring system;
FIG. 12A is a flow chart illustrating the method of the present invention for a vehicle intrusion detection system configuration of the vehicle interior monitoring system of FIG. 12;
FIG. 12B is a flow chart illustrating the method of the present invention for the compartment image data storage system configuration of the vehicle interior monitoring system of FIG. 12; and
FIG. 13A, 13B, 13C and 13D are flow charts illustrating the method of the present invention for controlling a vehicle lighting system.
FIG. 1A illustrates an automatic rearview mirror 1 comprising a variable reflectance mirror element 1a and a single rearwardly facing photosensor 2. The photosensor 2 is mounted facing rearwardly of the rearview mirror 1 so that its field of view encompasses an area comprising a rear window area and at least a portion of either or both side window areas. Also shown is a switch 3 to allow a driver to manually control several possible mirror functions, such as an on-off control switch, a sensitivity adjustment and a force-to-day or a force-to-night switch (i.e., forced maximum or minimum reflectance levels, respectively). An expanded view of the photosensor 2, which is preferably located in an upper center area of the variable reflectance mirror element 1a as shown, shows a light sensing and logic circuit 26 comprising a photosensor array 32 and a logic and control circuit 34 (which is not shown in FIG. 1A but is shown in FIG. 6 as discussed below). A photosensitive surface of each of the photosensor elements 32a (shown in FIG. 5) of the photosensor array 32 senses light levels or image information in a predetermined field of view encompassing an area located rearwardly of the rearview mirror 1. A lens 30 images or otherwise focuses the light information from the predetermined field of view onto the photosensor array 32.
The rearview mirror 1 further comprises a channel mount 1b or other mounting means used to fixedly attach the mirror 1 to the windshield or headliner area of the vehicle. The rearview mirror 1 is generally adjustable with respect to the channel mount 1b to allow a driver to position the mirror for correct viewing of the rearward area or scene so that the driver's sightline through the rearview mirror 1 is aligned approximately with the vehicle's centerline.
Preferably, the photosensor 2 is fixedly mounted on the adjustable portion of the rearview mirror 1 as shown in both FIGS. 1A and 1B so that the viewing axis of the photosensor 2 is generally aligned with the viewing axis of the mirror 1 which is perpendicular to the glass surface of the mirror 1. This approach is preferable both because of packaging concerns and because it provides a guaranteed sightline. It is, however, within the scope of the present invention to mount the photosensor array 32 so that it is movable with respect to the variable reflectance mirror element 1a of the rearview mirror 1.
More preferably, as shown in FIG. 1A, the photosensor 2 is located in the upper center area of the variable reflectance mirror element 1a. This may be required, for example, if it is necessary to reduce the bezel size of the rearview mirror 1. If the photosensor 2 is located behind a glass surface of the variable reflectance mirror element 1a, an appropriately sized hole is provided in the protective and reflective materials of the variable reflectance mirror element 1a. Additionally, a corresponding area within an active layer of the variable reflectance mirror element 1a may be removed or otherwise rendered inactive to enable the photosensor 2 to view directly the rearward scene. Alternatively, for manufacturing reasons, the photosensor 2 may view the rearward scene through the active layer of the variable reflectance mirror element 1a, in which case it is preferable to compensate for or otherwise negate the effects of reducing reflectance and correspondingly the transmittance of the variable reflectance mirror element 1a so that the photosensor 2 effectively views the rearward scene directly as will be described later.
Most preferably, a reflective surface is maintained within the hole to both preserve the cosmetic appearance of the assembly as viewed by the driver and to maximize the reflective surface. This can be achieved by providing a very thin metal reflective layer (100Å thickness or lower) of aluminum, stainless steel, chromium, or silver, etc., so as to be sufficiently transmitting for incident light to enable proper operation of the photosensor array 32 but also sufficiently reflective to appear mirror-like in the area of the hole. Alternatively, a reflective tape, which is both sufficiently transmitting and reflective to achieve the objectives described herein, may be adhered at the hole region using suitable means such as an optical adhesive and the photosensor array 32 may then be mounted behind the optical adhesive. Additionally, thin film stacks such as a solid state tri-layer of 1/4 wave TiO 2 ,1/4 wave SiO 2 and 1/4 wave TiO 2 or some other single thin film of a high index material may be mounted behind or coated upon the area of the hole. Finally, since the preferred photosensor array 32 is responsive to both visible light and near infrared, it is preferable to select a material which reflects a significant proportion of visible light while being essentially transparent to infrared.
As shown in FIG. 1B, the photosensor 2 may also be located in the bezel or chin of the rearview mirror 1 to view the rearward area directly without any compensation. In another preferred embodiment, the photosensor 2 may also be located on or near the channel mount or mounting bracket 1b so that the axis of the photosensor 2, which is perpendicular to the plane of the photosensor array 32, is in fixed alignment with the vehicle's centerline regardless of the adjusted position of the rearview mirror 1.
In particular, as shown in FIGS. 1C and 1D, a sensing and logic circuit assembly 27, which comprises a sensing and logic circuit 26 and the photosensor 2 and switch 3 on a printed circuit board, is located in a housing or module 7 that is attached, connected, made integral or otherwise associated with the rearview mirror 1. In the embodiment shown in FIGS. 1C and 1D, a mounting bracket 6 is fixed relative to the headliner area of the vehicle body in a header mount arrangement; and a rearview mirror head assembly 1h is adjusted by a spherical pivot 6d at the interface of the mounting bracket 6 and the rearview mirror head assembly 1h. The mounting bracket 6 may also be releasably attached to a mounting button (not shown) that is attached to the windshield to provide generally improved ease of assembly and replacement, as well as safety. Alternatively, the mounting bracket 6 may be attached to the windshield or headliner area of the vehicle by any of the various means well known to those skilled in the art.
In particular, the mounting bracket 6 comprises a retaining spring 6a, a retaining screw 6b, a wire harness opening 6c for receiving a wire harness assembly 8, and a spherical pivot 6d having an opening for wires 6e that are used to control the variable reflectance mirror element 1a. The housing or module 7 comprises a retaining housing or module 7a for partially mounting the sensing and logic circuit assembly 27, a rear housing or module cover 7b, a heat sink 7c for the sensing and logic circuit assembly 27, a screw 7d for securing the heat sink 7c to the mirror bracket 6, and a wire connector 7e for connecting the harness assembly 8 and wires 6e to the sensing and control circuit assembly 27. The harness assembly 8 is used, in part, to supply power to the sensing and logic circuit assembly 27.
Also, as shown in FIGS. 1C and 1D, the automatic rearview mirror 1 comprises the variable reflectance mirror element 1a, a mirror cushion support 1c, an impact absorber layer 1d, a bezel 1e, a mirror case if and clamp springs 1g for receiving and securing the spherical pivot 6d of the mounting bracket 6.
For other vehicles, such as trucks, the photosensor 2 may also be located with each of the external side view mirrors as will be described later.
The lens 30 is preferably a single molded plastic lens approximately 2 millimeters in diameter and is preferably bonded to or in close contact with the photosensor array 32. The lens 30 may, however, include any appropriate image focusing means such as conventional single component optics, holographic lens type optics, binary optics or a microlens. The lens 30 preferably is also designed to focus an image of the rearward scene within a field of view defined by a cone. The cone's centerline is perpendicular to the plane of the photosensor array 32 and the cone preferably has an included angle of approximately 100 degrees. Thus, the image is focused onto a circular area of the plane of the photosensor array 32. Of course, the photosensor array 32 could be positioned in other than a rearwardly facing direction so long as appropriate lenses or other optics are used to direct the light or image information from the rearward area onto the photosensitive surface of the photosensor array 32.
The pre-positioning of the photosensor array 32 in the rearview mirror 1 depends on whether the automatic rearview mirror system 20 is being used in a left hand or a right hand drive vehicle. In either case, the photosensor array 32 is preferably pre-positioned within the circular area of the focused image so that for either a left or right hand drive vehicle and with only driver adjustment of the rearview mirror 1, the rearward scene imaged onto the photosensitive surface of the photosensor array 32 includes the rear window area and at least a portion of the left and right side window areas of the vehicle.
If a sufficiently large photosensor array 32 is used, then the pre-positioning of the photosensor array 32 is not vehicle specific as described above, and a system 20 using a larger photosensor array 32 may be used for both left and right hand drive vehicles. The larger photosensor array 32 is positioned symmetrically within the circular area of the focused image described above. Using the larger photosensor array 32 involves using a pattern recognition means to determine the approximate vehicle centerline so that the appropriate portion of the larger photosensor array 32 may be selected depending on whether the automatic rearview mirror system 20 is installed in a left or right hand drive vehicle.
FIG. 2 illustrates an automatic rearview mirror system 20 for an automotive vehicle, comprising the rearview mirror 1, a left side view mirror 4 and a right side view mirror 5. As will be discussed below, either or both of the side view mirrors 4 and 5 may be connected to a control circuit of the rearview mirror 1. The mirrors 1, 4 and 5 may be constructed according to any of the methods known to those skilled in the art and are generally constructed according to the styling preferences and specifications of the automotive vehicle manufacturers. The means for mounting the rearview mirror 1, such as the channel mount 1b, and the electrical connectors used to connect the mirrors 4 and 5 to the control circuit of the rearview mirror 1 and the vehicle's electrical system may include any one of the many configurations known to those having ordinary skill in the art. The variable reflectance mirror element 1a of the mirrors 1, 4 and 5 may be any device having more than one reflectance level corresponding to a specific control or drive signal. Preferably, however, the variable reflectance mirror element 1a is an electrochromic mirror.
As discussed, the photosensor 2 is mounted facing rearwardly of the rearview mirror 1 so that its field of view encompasses an area comprising the rear window area and at least a portion of both the left side window area and the right side window area. The horizontal and vertical fields of view of the rearward area as seen by the photosensor 2, and more particularly by the photosensor array 32, are illustratively shown in FIGS. 3A and 3B.
As shown in FIG. 3A, the photosensor array 32 senses a field of view divided into three separate zones: a center zone a, a left zone b (generally corresponding to the left side window area) and a right zone c (generally corresponding to the right side window area). Each zone is sensed by a separate set or sub-array S(X) of photosensor elements 32a (described with respect to FIGS. 4A and 4B) within the photosensor array 32. The center zone, zone a, generally receives light from the rear window area of the vehicle. This rear window area is depicted by a trapezoidally shaped rear window figure superimposed on a first set or sub-array S(l) of photosensor elements 32a used to sense light levels in zone a. Zone b includes light from at least a portion of a left side window area. This is depicted by a trapezoidally shaped left rear side window figure and a partially shown left front side window figure superimposed on a second set or sub-array S(2) of photosensor elements 32a used to sense light levels in zone b. Similarly, zone c includes light from at least a portion of a right side window area. This is depicted by a trapezoidally shaped right rear side window figure and a partially shown right front side window figure superimposed on a third set or sub-array S(3) of photosensor elements 32a used to sense light levels in zone c. Additionally, all three zones include light reflected from whatever fixed body work and interior trim, head rests, vehicle occupants or other objects that are within the zones a, b and c.
Also as illustratively shown in FIG. 3A, the photosensor elements 32a in columns 1 to 4 comprise the third photosensor element set in zone c, the photosensor elements 32a in columns 6-11 comprise the first photosensor element set in zone a and the photosensor elements 32a in columns 13 to 16 comprise the second photosensor element set in zone b. Null zones are provided between the zones a and b and between the zones a and c to allow for driver adjustment of the rearview mirror 1. These null zones also ensure that the center zone a does not include light or other image information from the side window areas of zones b and c.
As will be discussed in more detail below, the logic and control circuit 34 selects photosensor element signals from the first photosensor element set or sub-array S(1) (shown in FIG. 4B) corresponding to zone a to control the reflectance level of the rearview mirror 1. Similarly, the control circuit 34 selects photosensor element signals from the second photosensor element set or sub-array S(2) (shown in FIG. 4B) corresponding to zone b to control the reflectance level of the left side view mirror 4, and further selects photosensor element signals from the third photosensor element set or sub-array S(3) (shown in FIG. 4B) corresponding to zone c to control the reflectance level of the right side view mirror 5. Additionally, for a variable reflectance mirror element 1a having segments, such as a center, left and right segment, appropriately defined zones a, b and c, i.e., sub-arrays S(1), S(2) and S(3), corresponding to the mirror segments may be used by the logic and control circuit 34 to control independently the individual mirror segments.
FIG. 3B illustratively shows the preferred embodiment for the zones of the photosensor array 32. In this embodiment, the logic and control circuit 34 selects photosensor element signals from three overlapping sets or sub-arrays S(1), S(2) and S(3) of photosensor elements 32a corresponding to the three overlapping zones a, b and c to control, respectively, the reflectance level of the mirrors 1, 4 and 5. More specifically, the control circuit 34 selects photosensor element signals from the photosensor elements 32a in columns 6 to 11 (zone a) to control the reflectance level of the rearview mirror 1. The control circuit 34 also selects photosensor element signals from photosensor elements 32a in columns 10 to 14 (zone b) to control the reflectance level of the left side view mirror 4, and further selects photosensor element signals from photosensor elements 32a in columns 3 to 7 (zone c) to control the reflectance level of the right side view mirror 5.
Additionally, in the FIG. 3B embodiment, the lens 30 focuses or images light information from: (1) the rear window area onto zone a; (2) at least a portion of the rear window and left side window areas onto zone b; and (3) at least a portion of the rear window and right side window areas onto zone c. Contrastingly, in the FIG. 3A embodiment, the lens 30 focuses light from: (1) the rear window area onto zone a; (2) the left side window area onto zone b; and (3) the right side window area onto zone c. The overlapping zones in the FIG. 3B embodiment are advantageous because each set of overlapping photosensor elements 32a in zones a and b and each set of overlapping photosensor elements 32a in zones a and c, as well as the logic and control circuit 34, is able to "preview" the light information that may, for example, first appear in the rear window area (and correspondingly in the rearview mirror 1), but which may appear shortly thereafter in the left or right side view mirrors 4 and 5. By examining at least a portion of the rear window area, the automatic rearview mirror system 20 is able to more quickly respond to annoying glare light from approaching vehicles or other sources. overlapping zones are also generally preferred because a glare light source located in a common or overlapping area of the rearview mirror 1 and one of the side view mirrors 4 or 5 can influence both mirrors.
The light sensing device of the light sensing and logic circuit 26 is preferably the photosensor array 32 shown in FIG. 5. The photosensor array 32 has sufficient resolution to view the real image of a scene but may also use a spatial distribution of light intensities as an approximation of the imaged scene. An example of such a photosensor array 32 is the VLSI Vision Limited (VVL) Single Chip Video Camera Model #ASIS 1011.
Since a photosensor array 32 of the type described, namely the VVL Single Chip Video Camera, is capable of providing image information having sufficient resolution for displaying an actual image or for some other purpose, it will be readily understood that additional features or functions may be incorporated by adding circuitry to provide video output from the photosensor array 32 in addition to the primary control functions described herein. For example, the video output may be output to a CRT, flat LC panel display or other appropriate display device, located within the vehicle, to provide a display of the imaged scene for viewing by the driver.
The photosensor array 32 may be located in any of the mirrors 28 or in any other appropriate location, whether local or remote, such as on the vehicle's rear bumper, thereby extending significantly the effective field of view normally available to the driver either directly or through the vehicle's mirrors 28. Additionally, the photosensor array 32 may even replace one or more of the side view mirrors 4 and 5 of the automatic rearview mirror system 20, thereby reducing the aerodynamic drag on the vehicle while providing sufficient information to the driver comparable to that available through the side view mirrors 4 and 5.
A video signal from the photosensor array 32 may also be used by the logic and control circuit 34 to determine the presence of a vehicle or other object within the field of view of the photosensor array 32 to provide a visual signal warning such as through a display panel, or even an audible warning, based on certain parameters, such as distance and speed of the object. Additionally, if the photosensor array 32 is located in the rearview mirror 1, the video signal may be used to monitor the vehicle's interior to detect unauthorized intrusion into the vehicle. This may be achieved by providing electrical power to the mirror's logic and control circuit 34 from a vehicle power supply and by activating a vehicle intrusion monitoring mode when a signal indicates that the vehicle's door and trunk locks have been activated. The logic and control circuit 34 may be used to continuously monitor the image from the vehicle's interior thereby allowing detection of objects or persons moving within the vehicle, and if movement is detected, another signal from the logic and control circuit 34 may then activate an intrusion alarm.
Thus, the photosensor array 32 may be used to monitor the vehicle interior or compartment in a vehicle interior monitoring system. This monitoring capability may be used in a vehicle intrusion detection system or in a compartment image data storage system, either in combination with the automatic rearview mirror system or as an independent system. Using the photosensor array 32 to monitor the vehicle interior to detect potential intruders provides an effective vehicle intrusion detection system. In an automatic rearview mirror and vehicle intrusion detection system, the photosensor array 32 in the rearview mirror 1 provides a good location for monitoring the vehicle interior because the rearview mirror 1 is: (1) centrally located along the vehicle axis; (2) forward of the front seat; and (3) relatively high in the vehicle interior. This location is sufficiently high and far forward so as to provide a very good view of the vehicle interior, including the front and rear seat areas, front and rear door areas and hatchback or rear cargo door areas. The photosensor array 32 may also be positioned in other locations, including the headliner and headliner console areas, for example, or any other appropriate location depending on the particular application.
As is discussed later, when the vehicle interior monitoring system is used as a vehicle intrusion detection system, the logic and control circuit 34 processes image data to detect motion or movement in the vehicle interior, establishes an intrusion condition if such motion is detected and outputs one or more control signals to vehicle hardware or to a vehicle controller system. Vehicles today are often equipped with such controller systems. These vehicle controller systems may be used to control the exterior lights, interior lights, horn (or siren), ignition or other such vehicle hardware. The logic and control circuit 34 therefore outputs one or more control signals to various vehicle hardware or to the vehicle controller system to activate the interior and exterior lights, horn or siren or to disable the ignition to deter intruders from stealing the vehicle or its contents. Other control output signals may activate RF beacon devices or similar devices within the vehicle so that the vehicle may be tracked, as will be further described later.
It is, however, within the scope of the present invention for the light sensing device to comprise any similarly appropriate image or array sensor. When the light sensing and logic circuit 26 is formed as a very-large-scale-integrated (VLSI) complementary-metal-oxide-semiconductor (CMOS) device, as is known to those skilled in the art, the light sensing device will share a common semiconductor substrate with the logic and control circuit 34.
Preferably, for the described three mirror system, the photosensor array 32 comprises a plurality of photosensor elements 32a arranged in 160 columns and 40 rows (a 160×40 array) providing a horizontal field of view of approximately 100 degrees and a vertical field of view of approximately 30 degrees. As discussed, FIGS. 3A and 3B illustratively show a 16×4 photosensor array 32. The photosensor array 32 may, however, comprise any appropriately sized array having an appropriate field of view. For example, the field of view may be narrower when controlling the segments of only one mirror. Each photosensor element 32a is preferably about 10 microns square.
As shown in FIG. 4A, the photosensor array 32 generally comprises a plurality of photosensor elements 32a arranged in a photosensor array PA(N,M) having N rows of M columns. When viewing the photosensitive surface of the photosensor array PA(N,M) in a vertical plane, the lower row is row 1, the top row is row N, the left hand column is column 1, and the right hand column is column M. A specific photosensor element is identified as E(n,m) and the signal indicative of a light level incident thereon is L(n,m). Also, the sub-array S(X), where X=0, 1, 2, . . . , Z, is a rectangular array having P(X) rows of Q(X) columns of photosensor elements 32a and is located such that its lower left hand element is photosensor element E(T(X),U(X)).
As shown in FIG. 4B, a background sub-array S(X) designated S(0) is used to determine a general background light level B. Signals from the photosensor elements 32a of each peak sub-array S(X), designated S(1), S(2), . . . , S(z), are used to determine a peak light level P(z) incident on each peak sub-array S(1), S(2), . . . , S(z). The general background light level B for background sub-array S(0) and the peak light level P(z) for each peak sub-array S(X) are then used to determine a mirror control signal V c (z) for controlling at least one mirror or mirror segments associated with each zone.
FIG. 5 generally illustrates a logic layout of the photosensor array 32. The logic and control circuit 34 generates array control signals to control the photosensor array 32. As is well known in the art, the photosensor array 32 is typically accessed in scan-line format, with the array 32 being read as consecutive rows, and within each row as consecutive columns or pixels. Each photosensor element 32a is connected to a common word-line 33e. To access the photosensor array 32, a vertical shift register 33a generates word-line signals for each word-line 33e to enable each row of photosensor elements 32a. Each column of photosensor elements 32a is connected to a bit-line 33f which is connected to a charge-to-voltage amplifier 33c. As each word-line 33e is accessed, a horizontal shift register 33b uses a line 33g to output the bit-line signals on consecutive bit-lines 33f to an output line 33h connected to the logic and control circuit 34. Also shown is a voltage amplifier 33d used to amplify the resulting analog photosensor element signals. The analog photosensor element signals are then output on line 33h to the analog-to-digital converter 44 and converted to digital photosensor element signals.
As discussed above, the photosensor array 32 is responsive to or senses both visible light and near infrared illumination. FIGS. 11A and 11B illustrate the normalized spectral response for two versions of the preferred photosensor array 32. In FIGS. 11A and 11B, visible light generally covers the wavelengths from about 400 nm to about 750 nm, while near infrared illumination or light generally covers the wavelengths from about 750 nm to about 3000 nm(not shown). More particularly, FIG. 11A illustrates the normalized spectral response of the preferred photosensor array 32 made using a non-epitaxial silicon process, where the peak spectral response occurs at about 800 nm. FIG. 11B shows the normalized spectral response of the preferred photosensor array 32 made using an epitaxial silicon process, where the peak spectral response occurs at about 650 nm. As shown, the non-epitaxial silicon photosensor array is more sensitive to near infrared illumination having wavelengths on the order of about 800 nm. The photosensor array 32 made using the non-epitaxial silicon process and having the normalized spectral response of FIG. 11A is most preferred in both the particular automatic rearview mirror and vehicle interior monitoring systems described herein. For automatic rearview mirror systems as described herein, this is because vehicle headlights generally provide significant levels of near infrared illumination. For vehicle interior monitoring systems as described herein, either natural sources (such as sunlight) or supplemental sources of near infrared illumination may be used to enhance the image information available to and the performance of such systems, as will be further discussed below.
The field of view and resolution of the photosensor array 32 depends on the number and physical dimensions of the photosensor elements 32a and on the design or geometry of the lens 30. For the lens type illustrated in FIG. 1A, the lens 30 may, for example, be designed to have an included angle on the order of up to about 140°. For the automatic rearview mirror system previously described, the effective field of view of approximately 100° horizontal and approximately 30° vertical is preferred. For the automatic rearview mirror and vehicle interior monitoring system described herein, an effective field of view of approximately 100° horizontal and approximately 75° vertical is preferred. Also as discussed for the automatic rearview mirror system, the lens 30 preferably focuses an image within a field of view defined by a cone having an included angle of approximately 100 degrees. Accordingly, when the lens 30 focuses the image onto the focal plane of the 160×40 photosensor array 32, the photosensor array 32 only falls within a segment of the focused image area.
FIG. 2A generally illustrates a view of a vehicle interior 100 (which includes the window areas of FIGS. 3A and 3B) as focused by the lens 30 and as viewed by a 160×120 photosensor array 32. Also shown are a driver or left seat 101, a front passenger or right seat 102, a rear window area 103a, a right side window area 103b and a left side window area 103c. The 160×40 photosensor array 32, however, only sees a portion or segment of the vehicle interior 100, as is shown in FIGS. 3A and 3B. In a dedicated automatic rearview mirror system, the 160×40 sized array is generally preferred since it provides sufficient image information for providing effective automatic rearview mirror control and because it reduces the cost of the photosensor array 32. If the photosensor array 32 is also used to monitor the vehicle interior 100 (or for other applications) as is described herein, then the larger 160×120 array size may be used to view the vehicle interior 100 as is generally illustrated in FIG. 2A.
Finally, it should be understood that the spatial resolution of the photosensor array 32 may also be increased. This may be done by making the photosensor elements 32a smaller so as to increase the number of photosensor elements 32a in a photosensor array 32 having the same physical dimensions. Additionally, spatial resolution may be increased by varying the lens 30 to decrease the included angle of the image cone so that the photosensor array 32 views a smaller portion of an image on the vehicle interior 100.
In summary, the array size of the photosensor array 32 and the number and physical dimensions of the size of the photosensor elements 32a and the lens design or geometry of lens 30 may all be varied to optimize the effective field of view of the photosensor array 32 depending on the application.
As is discussed later, an exposure time or exposure period EP of the photosensor array 32 may be varied over some range depending on the light level. Thus, the value of EP is increased for decreasing light levels and approaches a maximum for low light levels, and it is decreased for increasing light levels and approaches a minimum for high light levels. For a given value EP v of the exposure period, there is a light level LL MIN that is sufficiently distinct from low signal noise in the photosensor element signal L(n,m) of each photosensor element E(n,m) so that it may be accurately sensed, and there is also a light level LL MAX for which the photosensor element signal L(n,m) of each photosensor element E(n,m) is a maximum. The ratio of LL MAX /LL MIN at EP v may be used to represent a dynamic range of DR(n,m) in decibel (dB) units of each photosensor element E(n,m), where DR(dB) =10 LOG (LL MAX /LL MIN ). The image data is preferably optimized such that it is approximately centered within the dynamic range DR(N,M) of the photosensor array 32. This may be done by determining an array response AR of RA(N,M), which is described later, where the minimum and maximum digital values of AR correspond to the minimum and maximum digital values possible for Val RA(n,m) (e.g., 0 and 255 for 8-bit data resolution). The exposure period is varied or adjusted until AR approaches the center or mid-point of the possible data value range (e.g., 127 for 8-bit data resolution).
Since there is a minimum photosensor element signal that may be accurately measured, a supplemental source of illumination may be desirable or necessary to enhance the effective sensing capabilities of the photosensor array 32 by providing supplemental source illumination SSI. Although the photosensor array 32 is able to monitor the vehicle interior 100 over a range of background lighting levels from about 0.1 lux (a dark garage) to about 30-60K lux (a bright, sunny day), using either visible or near infrared SSI to illuminate the vehicle interior 100 generally (or specific areas therein) significantly enhances the effectiveness or performance of the photosensor array 32 in various applications. Also, SSI is preferably provided only during the exposure period EP of the photosensor array 32 rather than continuously. Pulsed SSI reduces power consumption, extends the life of the supplemental source of illumination and provides generally higher instantaneous illumination than may be provided by continuous illumination. Also, pulsed infrared SSI is generally more difficult to detect by infrared illumination sensing apparatus that may be used by potential intruders.
For the specific vehicle interior monitoring system applications described herein, near infrared illumination between about 700 and 1200 nm is preferred because: (1) it is visible to the photosensor array 32 but not to the human eye (see FIGS. 11A and 11B); and (2) it does not affect adaption of the human eye. There are a number of readily available near infrared illumination sources, including solid-state sources such as light emitting diodes (LEDs) and lasers, flash lamps such as xenon or krypton lamps, incandescent lamps such as tungsten lamps, as well as many others. Preferred, however, are gallium arsenide (GaAs) or gallium aluminum arsenide (GaAlAs) LEDs because they provide a relatively narrow band (about 750 to 950 nm) of near infrared illumination (see FIGS. 11A and 11B). Such illumination sources are also typically packaged with a lens to distribute the illumination. Depending on the particular application, the illumination distribution characteristics of readily available lens/source packages may range from narrow so as to provide spot or collimated illumination to very diffuse so as to cover about 160°. In the vehicle interior monitoring system described herein, the lens/source package preferably provides illumination coverage on the order of about 100°.
Other illumination sources providing broad-band illumination (ultraviolet through infrared) may also be used, but it may be desirable or necessary to filter such broad-band illumination using absorption or interference type filters, or any other appropriate filter. In particular, an interference filter known as a long-wave pass filter or cold mirror reflects visible light, transmits infrared illumination and looks like the normal silvered mirrors typically used in the rearview mirror 1. Unlike cold mirrors, however, silvered mirrors reflect near infrared illumination. Since the cold mirror resembles the silvered mirror in the rearview mirror 1, it may be used to replace a section or even all of the silvered mirror. In particular, the supplemental source of illumination may be located behind the cold mirror element and adjacent to the photosensor array 32 with an opaque barrier separating the two to prevent supplemental illumination reflections within the rearview mirror 1 from directly affecting the photosensor array 32.
Alternatively, a long-wave pass absorption filter may be used with a supplemental source of broad-band infrared illumination. Long-wave pass absorption filters may be fabricated using a wide variety of polymers having appropriate optical transmission characteristics such as epoxies, acrylics, polycarbonates, as well as a variety of glasses. The acrylic and polycarbonate polymers are preferred because they are environmentally stable, cost effective and because they may be used to injection mold parts having various geometric shapes or polished or textured surfaces. Using absorption filter materials, the photosensor array 32 and supplemental source of illumination may be integrated into the rearview mirror 1 or elsewhere within or on the vehicle so that they are not readily apparent to vehicle occupants, passers-by or potential intruders.
FIG. 6 shows the light sensing and logic circuit 26 comprising the photosensor array 32 and the logic and control circuit 34. The logic and control circuit 34 comprises a logic circuit 46, a clock 47, a random-access-memory (RAM) 50, or other appropriate memory, and a digital-to-analog converter 52. The logic circuit 46 is preferably a dedicated configuration of digital logic elements constructed on the same semiconductor substrate as the photosensor array 32. Alternatively, the logic circuit 46 may also be a microprocessor comprising a central processing unit (CPU) and a read-only-memory (ROM). The logic circuit 46 may also be implemented using gate array technology or any other appropriate hardwired logic circuit technology.
The logic circuit 46 interfaces with the clock 47, provides array control signals to the photosensor array 32, manages data flow to and from the RAM 50 and converters 44 and 52, and performs all computations for determining a digital mirror control signal V DAC (z) for causing the variable reflectance mirror element 1a to assume a desired reflectance level. As discussed, the analog-to-digital converter 44 converts the analog photosensor element signals to the digital photosensor element signals processed by the logic circuit 46. It has been found that an eight-bit analog-to-digital converter 44 provides adequate data resolution for controlling the mirrors 1, 4 and 5. Preferably, the analog-to-digital converter 44 is constructed on the same semiconductor substrate as the photosensor array 32 as shown in FIG. 5.
The digital photosensor element signals output to the logic and control circuit 34 are generally stored in the RAM 50 for processing. The values of the digital photosensor element signals for the photosensor array PA(N,M) are correspondingly stored in an array in the RAM 50 designated RA(N,M). The logic circuit 46 processes the values of each of the digital photosensor element signals, which are designated Val RA(n,m), to determine an instantaneous or substantially real-time background light signal B t for a time period t and at least one peak light signal P(z). The logic circuit 46 uses these signals, which may also be temporarily stored in the RAM 50, to determine a digital control signal V DAC (z) to cause at least one mirror or mirror segment to assume a desired reflectance level. The digital mirror control signal V DAC (z) is then output to the digital-to-analog converter 52, which outputs a corresponding analog mirror control signal V c (z) to a mirror drive circuit 24. Alternatively, the digital-to-analog converter 52 need not be used if the logic circuit 46 generates a pulse-width-modulated (PWM) mirror control signal to control the mirror drive circuit 24.
The mirror drive circuit 24 comprises mirror drive circuits 24a, 24b and 24c. The drive circuit 24 drives mirrors 28, which comprises a rearview mirror 28a (mirror A), a left side view mirror 28b (mirror B) and a right side view mirror 28c (mirror C). Mirrors A, B and C correspond, respectively, to the rearview mirror 1, the left side view mirror 4 and the right side view mirror 5 shown in FIG. 2. It is, of course, within the scope of the present invention for the mirror A to be a mirror other than the rearview mirror 1. It is similarly within the scope of the present invention for the mirror B to be a mirror other than the left side view mirror 4, and for the mirror C to be a mirror other than the right side view mirror 5. It is also within the scope of the invention for the mirrors A, B and C to be mirror segments or zones of the variable reflectance mirror element 1a where the peak sub-array S(X) for each zone corresponds to a segment of the variable reflectance mirror element 1a. Thus, for example, S(1) may correspond to a center mirror segment, S(2) may correspond to a left mirror segment and S(3) may correspond to a right mirror segment. Any other appropriate mirror segmentation scheme may also be used.
A sensitivity control circuit 42 is used to input a sensitivity signal S to the logic and control circuit 34. In addition, signals from a force-to-day (maximum reflectance) switch 36, a reverse-inhibit (maximum reflectance) switch 38 and a force-to-night (minimum reflectance) switch 40 may also be input to the logic and control circuit 34. The switch 3 of FIGS. 1A and 1B may include the sensitivity control circuit 42, as well as the force-to-day switch 36 and the force-tonight switch 40.
The switches 36, 38 and 40 each generate a signal causing the logic circuit 46 to override its normal operation, as will be described with respect to FIGS. 7, 8A and 8B, and to output mirror control signals V c (z) to the mirror drive circuit 24 causing the variable reflectance mirror 28 to assume a maximum or minimum reflectance level in accordance with the appropriate signals from the switches 36, 38 or 40.
Finally, the logic and control circuit 34 may also be used to control a vehicle lighting switch 45 to automatically turn on and off a vehicle's headlights and sidelights. This feature will be further described later.
FIG. 6A shows the block schematic diagram of the automatic rearview mirror and vehicle interior monitoring system. The previous description of FIG. 6 applies here except as follows. First, the logic and control circuit 34 includes an analog-to-digital converter 55 for converting one or more analog control input signals 70 (1, 2, . . . , N; blocks 70a to 70n ) to digital signals that are input to the logic circuit 46.
With respect to the automatic rearview mirror system, the analog control input signals 70 may include any analog control input signal used therein, including, for example, analog versions of the control input signals provided by the force-to-day-switch 36, reverse-inhibit-switch 38, force-to-night-switch 40 or sensitivity control circuit 42 of FIG. 6. Of course, digital versions of these same control input signals may also be input to the logic circuit 46 as digital control input signals 75 (1, 2, . . . , N; blocks 75a to 75n). The analog control output signals 80 (1, 2, . . . , N; blocks 80a to 80n) may include any analog control output signal used in the automatic rearview mirror system, including the analog mirror control signals V c (z). The analog circuits/switches 81 (1, 2, . . . , N; blocks 81a to 81n) may include the drive mirror circuits 24 that are used to drive the variable reflectance mirrors 28. As discussed with respect to FIG. 6, the analog mirror control signal V c (z) is output to the mirror drive circuit 24 causing the variable reflectance mirror 28 to change reflectance levels. Of course, digital control output signals 85 (1, 2, . N; blocks 85a to 85n) may also be output to digital circuits/switches 86 (1, 2, . . . , N; blocks 86a to 86n) to the extent that the control output signals are digital and not analog.
With respect: to the vehicle interior monitoring system configured as a vehicle intrusion detection system, analog control input signals 70 and digital control input signals 75 may include, respectively, analog and digital versions of control input signals used to "arm" or "alert" the vehicle intrusion detection system, as will be further described later. The analog control output signals 80 may include any analog control signals output to analog circuits/switches 81 that are used in the above system, including analog circuits or switches used to actuate various vehicle hardware, such as the vehicle horn (or siren), exterior and interior lights or ignition control devices. Of course, digital control output signals 85 (1, 2, . . . , N; blocks 85a to 85n) may also be output to digital circuits/switches 86 (1, 2, . . . , N; blocks 86a to 86n) to the extent that the control output signals are digital and not analog. In particular, the digital control output signal 85 may include a digital word provided to a digital circuit/switch 86 that is a vehicle controller system that interfaces with such vehicle hardware.
When the vehicle interior monitoring system is configured as a compartment image data storage system, a nonvolatile memory 57, as shown in FIG. 6A, is included. The nonvolatile memory 57 interfaces with the logic circuit 46. The nonvolatile memory 57 is used to store image data, as will be further described later. The nonvolatile memory 57 may be an EEPROM or other appropriate nonvolatile memory. An access/security decoding logic circuit 58 interfaces with a data access port 59 and the logic circuit 46. The access/security decoding logic circuit 58 and data access port 59 are used to access the image data stored in the nonvolatile memory 57, as will be further described later. Optionally, this system may include a data compression logic circuit 56 for compressing image data received from the logic circuit 46 before it is stored in the nonvolatile memory 57. The data compression logic circuit 56 may be integral with the logic circuit 46.
Finally, whether configured as a vehicle intrusion detection system or as a compartment image data storage system, the vehicle interior monitoring system preferably includes a supplemental source of illumination 61 having a lens 62 as shown in FIG. 6A. A supplemental source of illumination drive circuit 60 is connected to the supplemental source of illumination 61. The drive circuit 60 also interfaces with and receives control signals from the logic circuit 46 to drive the supplemental source of illumination 61.
FIG. 7 shows an overview of the logic flow chart and method for controlling the reflectance levels of any one or all of the mirrors or mirror segments 28a, 28b or 28c. It should be understood that the reflectance level of each of the mirrors 28a, 28b and 28c in the automatic rearview mirror system of the present invention may be commonly or independently controlled. FIGS. 8A, 8B and 9 provide more detail on the logic and method of FIG. 7.
In step S101 of FIG. 7, light information seen rearwardly of the rearview mirror 1 is incident on the lens 30. In step S110, light passing through the lens 30 is refracted such that the light information is imaged or focused onto the photosensitive surface of the photosensor array 32. In step S120, the logic circuit 46 generates and outputs the array control signals to the photosensor array 32. In step S130, photosensor element signals indicative of the light levels incident on each of the photosensor elements 32a are generated. In step S140, these photosensor element signals are temporarily stored in RAM or any other appropriate memory. In steps S150 and S160, the logic circuit 46 determines values for the background light signal and the peak light signal for each zone corresponding to each of the mirrors 28. In step S180, the logic circuit 46 uses the background and peak light signals of step S150 to determine the control signals required to cause each of the mirrors 28 to achieve a desired reflectance level. Also, the logic and control circuit 34 in step S180 reads and processes the states of the optional sensitivity control circuit 42, force-to-day switch 36, force-to-night switch 40 and reverse-inhibit switch 38. In step S200, the mirror drive circuits 24 use the control signals determined in step S180 to generate drive signals to cause the mirrors 28 to assume the desired reflectance levels in step S210.
In one embodiment of the invention, the logic circuit 46 determines the background light signal B t in steps S150 and S160 by calculating the average value of the photosensor element signals, previously stored in RAM in step S140, for the photosensor elements 32a in a lowest row or rows of the photosensor array 32 corresponding to an area below the rear window. With respect to FIGS. 3A and 3B, this means that the background light signal B t is determined from photosensor element signals generated by the photosensor elements 32a located in row D of the photosensor matrix array 32. The logic circuit 46 may then output B t to the RAM 50 for later processing. The logic circuit 46 may also determine B t by calculating an average value of all of the photosensor element signals in the entire photosensor array 32. More generally, the background light signal B t for the rearward scene may be determined by calculating the average value of X percent of the lowest photosensor element signal values in the RAM array RA(N,M), where X is preferably 75, but typically may be in the range of 5 to 100. Alternatively, an exposure period EP, as is described herein, may be used to determine the background light signal B t . An array response AR may be determined using an array average method, as is also described herein, for the photosensor element signal values corresponding to a sub-array S(X) of the photosensor elements 32a of the photosensor array 32 that correspond to an area below the rear window. The exposure period EP may be varied within an operating point range OP±R, where OP is 10 and R is 5 (8-bit data), but where OP may be from 5 to 175 and R may be from 2 to 15. The exposure period is varied to maintain AR within OP±R. The background light signal B t may therefore be determined where B t varies inversely with EP.
Additionally, the background light signal B t is preferably change-limited to determine a limited background light signal B Lt . The signal B t may be change-limited, for example, by limiting changes in the background light signal B t to 2% per time frame. A time frame may be, for example, 250 milliseconds or any other time relating to the rate at which the logic circuit 46 samples the photosensor element signals from the photosensor array 32. The logic circuit 46 determines the change-limited value B Lt used to determine the digital mirror control signal V DAC (z) as follows: B Lt =B L (t-1) +C L X (B t -B L (t-1), where B Lt = the change-limited background light signal for a current time frame t, B t = the actual or substantially real-time background light signal for the current time frame t, B L (t-1) = the change-limited background light signal for a previous time frame (t-1) and CL= the change-limit value. Additionally, the background light signal B t from step S150 may be processed by the logic circuit 46 to determine whether the change limited background light signal B Lt is less than or greater than B L (t-1). If B Lt is greater than B L (t-1), then the logic circuit 46 may use a higher change-limit value C LH to determine B Lt . If the background light signal B Lt is less than or equal to B L (t-1), then the logic circuit 46 may use a lower change-limit value C LL to determine B Lt . The values C LH and C LL are in the range of 0.01 to 2, but are preferably on the order of about 0.02 or 2%.
The logic circuit 46 in step S150 also determines the peak light signal P(z) for each zone or sub-array S(X) of the photosensor matrix array 32. The peak light signal P(z) used to determine the appropriate mirror control signal V c (z) for the mirror 28 may be determined by counting or summing the number of occurrences where the digital value for a photosensor element signal is greater than a peak threshold value F for each zone or sub-array S(X). For the preferred analog-to-digital converter having eight-bit data resolution, the logic circuit 46 generates digital values indicative of light levels of light incident on each photosensor element 32a in the range of 0 to 255 (2 8 -1=255), with headlights resulting in values in the range of about 200 to 255, so that the peak threshold value F is selected to be in the range of about 200 to 255 but is preferably 245. The resulting count or sum P(z) provides a measure of the peak light level for the following reasons.
One design objective of the lens 30 and the photosensor array 32 combination is to be able to measure background light levels in the approximate range of 0.01 to 0.1 lux when driving on sufficiently dark roads. This is achieved by ensuring that the lens 30, photosensor elements 32a and charge-to-voltage amplifiers 33c are able to measure such light levels and by providing a maximum exposure time. The maximum exposure time determines the operating frequency or sampling rate of the system 20. In the case of the described system, 1.5 MHz has been found to be appropriate.
By varying the exposure time relative to a general background light level B and using a substantially constant sampling rate, a wide range of background light levels in the range of 0.01 to 1000 lux can be measured. Thus, when the background light level is low, the exposure time is relatively long such that headlights within the rearward area cause the affected photosensor elements 32a to saturate. Correspondingly, for higher background light levels, the exposure time is reduced. Saturation occurs when the incident light charges the photosensor element 32a to capacity so that any excess charge will leak or transfer to adjacent photosensor elements 32a. This charge leakage effect is commonly referred to as "blooming." It has been found that a count of the number of photosensor elements 32a at or near saturation, i.e., those having digital values greater than the peak threshold value F, provides an excellent approximation of the peak light levels and is further described in FIG. 8A. The above described method effectively extends the range of measurable light levels for the photosensor array 32.
As discussed, photosensor element signals are indicative of the incident light level or intensity and the time period for which they are exposed to such light. By operating the photosensor array 32 for a known exposure time or exposure period EP, the incident light intensity may be determined from the photosensor element signal generated by each photosensor element 32a. After the exposure period, the logic and control circuit 34 processes all of the photosensor element signals for each photosensor element 32a of the photosensor array 32. This signal processing at least includes the process of storing the digital value of each photosensor element signal to obtain RA(N,M), but normally includes all other processing for each image data set RA(N,M) up to and including the generation of output control signals, such as the mirror control signal V c (z). The time from the beginning of the exposure period EP through the processing of each image data set RA(N,M) and the generation of the appropriate output control signals is referred to as the operating or sampling period, and the frequency thereof is referred to as the operating frequency or sampling rate. The frequency at which the process is repeated may also be referred to as the frame rate or the image sampling frequency. The rate of each sub-process (e.g., exposure period) within the sampling period is controlled by the system clock 47. Thus, the frame rate or image sampling frequency is essentially fixed for a particular system clock frequency. The total period corresponds to a maximum exposure period EP and the total processing time relating to an image data set RA(N,M). The system clock frequency may be adjusted to scale the image sampling frequency, thereby adjusting EP. In summary, the maximum exposure period, the operating or sampling period, the signal processing time and the frequency of the system clock 47 should be considered in each application.
Alternatively, if an anti-blooming device is incorporated in the photosensor array 32, such as is well known to those skilled in the art, then the peak light signal P(z) may be determined by calculating an average value of Y percent of the highest photosensor element signal values for each zone, where Y is preferably 10, but may be in the range of 1 to 25. When using this approach for determining P(z), it is also preferable to include logic to adjust the sampling rate or operating frequency of the logic circuit 46 to an appropriate value depending on B Lt .
The general background light signal B, whether B t or B Lt , and the peak light signal P(z) for each zone of the photosensor array 32, as determined in steps S150 and S160, are then used by the logic circuit 46 to determine a mirror control signal V c (z) as a function of the ratio of B n (n preferably has a value of one but may typically range from 0.8 to 1.3) to P(z), i.e., V c (z)=f(B n /P(z)). The control signal V c (z) is then output to the mirror drive circuits 24 in step S180 to drive the mirrors 28 or segments thereof to their desired reflectance level in the steps S200 and S210.
FIG. 12 shows the logic flow chart and method for the vehicle interior monitoring system or mode.
In step S301, the logic circuit 46 initializes the system, sets EP to its maximum and if used, SSI to a predetermined minimum, such as zero. Next in step S310, the logic circuit 46 reads any analog control input signals 70 (70a to 70n of FIG. 6A) and/or digital control input signals 75 (75a to 75n of FIG. 6A) that may be used in the vehicle interior monitoring mode.
In step S315, the photosensor element signals are generated, processed and stored in RAM 50 by the logic circuit 46 (see steps S101 to S140 of FIG. 7). The logic circuit 46 also applies the lens correction factor LC(n,m) to each digital value Val RA(n,m) indicative of the photosensor element signal L(n,m) of each photosensor element 32a in the RAM array RA(N,M) to correct for the effect of lens 30. This results in RA(N,M) containing the lens corrected digital value Val RA Lc (n,m) indicative of the photosensor element signal of each photosensor element 32a.
Next, in step S320, the logic circuit 46 determines the array response AR, which is indicative of either RA(N,M) (an entire image data frame or set RA (t) at time t) or of a selected sub-array or sub-set thereof RS(N s ,M s ) (a partial image data frame or set RS (t) at time t) , where N s and M s are the row and column dimensions corresponding to a selected sub-array S(X) of the photosensor array 32. The logic circuit 46 processes the image data frame RA (t) using one of the methods described below to determine the array response AR. An appropriate operating point range OP±R is associated with each AR calculation method.
The preferred method for determining AR is the array average method, in which the logic circuit 46 determines AR by averaging all of the data values Val RA LC (n,m) in the image data frame RA (t) (or selected sub-array RS (t)) where: ##EQU1##
for n=1 to N, m=1 to M. Using the array average method, it has been found that appropriate OP and R values are 127 and 20 (8-bit data resolution), respectively; however, the operating point range may be non-symmetrical for some tasks by using non-symmetrical R values, such as +20 and -10.
An alternative method is the "no saturation" method, in which EP is set to its highest level at which there is no saturation or blooming in any photosensor element 32a. In this case, the logic circuit 46 reduces EP until the peak value of RA (t) or RS (t) is within the operating point range OP±R. It has been found that appropriate OP and R values are 249 and 5, respectively. Still another method involves maximizing the useful image area, in which the logic circuit 46 determines AR by determining the difference between the number of photosensor elements 32a having digital values of 0 and the number having digital values of 255 (8-bit data resolution). In this case, appropriate OP and R values are 0 and 5% of the number of photosensor elements 32a corresponding to the image data set RA (t) or sub-array RS (t). It should be understood that the specific values, such as 127 and 255, are based on 8-bit data resolution and would be appropriately scaled for other data resolutions.
In step S330 and S360, it is determined whether AR is in the operating point range OP±R. If AR is outside the range, then the image data frame is either too bright (AR>OP+R) or too dim (AR<OP-R) and EP and SSI are incrementally increased or decreased according to steps S340, S341, S342 or S350, S351, S352. This is repeated for every image data frame RA (t). The system thus optimizes EP and SSI for the particular circumstances at system startup, and thereafter continues to adjust EP and SSI to maintain AR within the operating point range OP±R as lighting conditions change.
If AR is within the operating point range OP±R, then the vehicle interior monitoring system/mode enters a primary task routine or mode in step S370, such as the vehicle intrusion detection system/mode (S400) of FIG. 12A or the compartment image data storage system/mode (S500) of FIG. 12B. After completing the primary task routine, the program returns to the vehicle interior monitoring mode to generate and store another image data frame RA (t).
The general lighting conditions of the rearward scene can be defined as follows: the background light level of the viewed rearward scene is B and the peak light level for each zone or sub-array S(X) is P(z). A contrast ratio C(z) may be defined as the ratio of the peak light level P(z) for each zone to the general background light level B; thus, C(z)=P(z)/B. Given the background light level B, the human eye can tolerate varying peak light levels in the viewed rearward scene up to a particular contrast ratio tolerance C T . Contrast ratios greater than C T initially cause discomfort and are generally known as glare. As the eye adjusts its light sensitivity to protect itself from the discomforting peak or glare light levels, vision is reduced and the glare may become disabling. Thus, the maximum tolerable peak light level P T of the viewed rearward scene is equal to the product of the contrast ratio tolerance C T and the background light level B, i.e., P T =C T ×B.
The desired reflectance R d (z) of a variable reflectance mirror for each zone is that reflectance level which reduces a peak light level P(z) to a value equal to the maximum tolerable peak light level P T , i.e., P T =R d (z)×P (z) or R d (z)=P T /P(z), and substituting the expression for P T , R d (z)=(C T ×B)/P(z) . However, the maximum tolerable contrast ratio C T varies across the population due to aging and other factors; accordingly, a sensitivity factor S may be used to account for this variation in contrast tolerance sensitivity so that R d (z)=(S×C T ×B)/P(z). Selecting the desired reflectance R d (z) for each zone provides maximum information from the rearward scene viewed in each mirror or mirror segment while reducing discomforting or disabling peak light levels to tolerable levels.
The mirror control signal V c (z) required to obtain the desired reflectance R d (z) depends on the particular variable reflectance mirror element that is used. For electrochromic mirrors, a voltage-reflectance relationship can be approximated and generally defined. In general, an electrochromic mirror has a reflectance level R having a maximum value of R 1 with an applied voltage V app of 0 volts. As the applied voltage V app is increased, the reflectance level R perceptually remains on the order of R 1 until V app reaches a value of approximately V 1 . As V app is further increased, the reflectance level R decreases approximately linearly until a minimum reflectance of approximately R 2 is reached at a voltage V 2 . Thus, the applied voltage V app can be approximately defined as: V app =V 1 +(R 1 -R)×(V 2 -V 1 )/(R 1 -R 2 )
Substituting desired reflectance R d (z) for the reflectance R results in the mirror control signal, the voltage of which is determined as follows: V c (z)=V 1 +(R 1 -S±C T ×B/P(z) )×(V 2 -V 1 )/(R 1 -R 2 ).
To obtain a digital value V DAC (z), V c (z) is scaled by a factor that is the ratio of the maximum digital value to the value V 2 ; thus, for eight-bit data resolution V DAC (z)=255 V c (z)/V 2 , and substituting for V c (z): V DAC (z)=255(V 1 +(R 1 -S×C T ×B/P(z))×(V 2 -V 1 )/(R 1 -R 2 ))/V 2 .
FIG. 8A provides further detail on the steps S150 and S160 where the logic circuit 46 determines the background and peak light signals. More particularly, steps S151, S152, S159 and S160 provide two processing loops for sequentially determining the digital values indicative of the photosensor element signals, Val RA(n,m), in the RAM array RA(N,M) for each of the photosensor elements 32a of the photosensor array PA(N,M).
In step S153, a lens correction factor LC(n,m) is applied to each digital value indicative of the photosensor element signal, Val RA(n,m), to correct for the effects of lens 30, which results in a lens corrected digital value of the photosensor element signal Val RA LC (n,m). These effects are typically referred to as cosine effects or Lambert's Law effects. The lens correction factor LC(n,m) depends on the radial distance of the photosensor element 32a from a central axis of the lens 30, and is typically in the range of 1 to 15 but will depend on the geometry of the lens and the selected photosensor array. The lens correction factor LC(n,m) applied to each Val RA(n,m) may be calculated according to Lambert's Law each time Val RA(n,m) is processed. More preferably, the logic circuit 46 initially stores an array of values LC(n,m) in the RAM 50 for each photosensor element 32a of the photosensor array PA(n,m) during an initialization routine. Alternatively, the size of the photosensor elements 32a of the photosensor array 32 may be adjusted to correct for the lens effects at each photosensor element 32a.
As discussed, it has been found that light levels for headlights generally result in an eight-bit digital value greater than a peak threshold value F having a value of about 245. Correspondingly, during non-daylight operation of the automatic rearview mirror system 20, background light levels generally result in eight-bit digital values indicative of the light levels incident on the photosensor elements 32a that are less than or equal to the peak threshold value F.
Accordingly, the lens corrected value Val RA LC (n,m) is compared in step S154 to the peak threshold value F. If Val RA LC (n,m) is less than or equal to F it is used to increment a counter B Count , in the logic circuit 46, by 1 in step S157 (thereby indicating that a va